CN1960198A

CN1960198A - Analysis method of sub carrier wave, bits, power in use for orthogonal frequency division multiple access system

Info

Publication number: CN1960198A
Application number: CNA2006101521675A
Authority: CN
Inventors: 田辉; 张平; 高有军; 徐海博; 陶小峰; 谢怀遥
Original assignee: Beijing University of Posts and Telecommunications
Current assignee: BEIJING STARPOINT TECHNOLOGY Co Ltd
Priority date: 2006-09-15
Filing date: 2006-09-15
Publication date: 2007-05-09
Anticipated expiration: 2026-09-15
Also published as: CN1960198B

Abstract

The method includes the following steps: distributing the sub-carrier number on the base of the power reduction value while the user adds a sub-carrier so as to decide the sub-carrier number needed by users; according to this decided number, calculating the mean bit number on a sub-carrier sent by all users; according to the power needed for sending this mean bit number, distributing the practical sub-carrier to all users. Via water injection algorithm of single user, the method carries out bit-loads for every user.

Description

Subcarrier, bit and power distribution method for orthogonal frequency division multiple access system

Technical Field

The present invention relates to an Orthogonal Frequency Division Multiple Access (OFDMA) system, and more particularly, to a subcarrier, bit, and power allocation method for an OFDMA system.

Background

With the rapid development of mobile communication technology and the rapid increase of user demand, multimedia services such as audio, video, image, and internet will become the leading services of future mobile communication, and the requirements of these services for the transmission capability of wireless link are significantly increased (peak service rate is greater than 20Mbps), in this case, Orthogonal Frequency Division Multiplexing (OFDM) technology is gradually emerging. OFDM technology modulates a high-speed data stream into multiple parallel low-speed data streams that are spectrally overlapped for transmission. Since the OFDM symbol period is significantly increased, the resistance of the OFDM symbol to multipath delay is improved, and inter-symbol interference (ISI) caused by multipath delay can be completely removed by introducing a guard interval, the OFDM technique has been adopted by several standards at present, and has been basically recognized as one of physical layer basic techniques of B3G (super-third generation mobile communication system). An Orthogonal Frequency Division Multiple Access (OFDMA) system is one of multiple access schemes that may be most likely used in a B3G system because an orthogonal adjacent subcarrier is flexibly allocated to different users, so that simultaneous access of multiple users is realized in a communication system, system capacity is improved, a resource allocation scheme can be dynamically changed, and rate transmission capability in a large dynamic range and quality of service (QoS) requirements of multiple users and multiple services in a future mobile communication system are met.

For the subcarrier, bit and power allocation method of the OFDMA system, the method with better performance in the prior art is a multi-user greedy water injection method. The method firstly allocates bits to be transmitted to all subcarriers according to a single-user water filling algorithm for transmission, then lists the subcarriers allocated to a plurality of users simultaneously as 'collision subcarriers' according to the principle that a plurality of users cannot share one subcarrier simultaneously, and then reallocates the bits loaded on the 'collision subcarriers' to other subcarriers, thereby causing the increase of power, most seriously causing complex processing procedures caused for solving the 'collision subcarriers', and the allocation method cannot meet the requirements of improving the system performance and reducing the cost of a future mobile communication system.

Disclosure of Invention

The task of the present invention is to provide a low-complexity subcarrier, bit and power allocation method for an Orthogonal Frequency Division Multiple Access (OFDMA) system, which significantly reduces the power consumption of information transmitted by a transmitting end of a communication system and the complexity of radio resource allocation, thereby improving the performance of the communication system and reducing the economic cost.

In the subcarrier, bit and power allocation method according to the present invention, the number of subcarriers required for each user is first determined. In order to ensure the fairness of users, the number of subcarriers allocated to each user is assumed to be 1, the average channel gain of each user is firstly calculated by combining channel information, then subcarriers are added to the users one by one according to the idea of the water injection principle, and the number of the subcarriers of the user with the largest transmission power reduction after one subcarrier is added by 1 until the number of all the subcarriers is completely allocated in each user.

The subcarriers specifically allocated to the user are then determined. According to the number of subcarriers already allocated to the users, the average number of bits sent by each user on each subcarrier can be obtained, and for each user, the power required for sending the number of bits on each subcarrier can be further obtained; and traversing all users, finding out the subcarrier with the minimum required transmitting power and the corresponding user thereof, then allocating the subcarrier to the user, and continuously allocating the rest subcarriers by adopting the same method until the subcarriers are all allocated to the user. In order to further reduce the complexity of the operation, in this step, the subcarriers may be allocated according to the channel gain corresponding to each subcarrier, that is, all users are traversed, the subcarrier corresponding to the maximum channel gain is found and allocated to the corresponding user, and the remaining subcarriers are continuously allocated by the same method until all subcarriers are allocated to the users.

And transmitting the bits required to be transmitted by each user on the allocated subcarriers according to a single-user water filling algorithm.

The method of the invention combines the channel information, adopts three steps to reduce the power required by the sending end when sending the information, each step leads the sending power to be the minimum in average meaning, and the three-step combined distribution scheme can also achieve the obvious reduction of the complexity. Therefore, the method according to the invention not only achieves low complexity, but also has better performance than other allocation methods.

According to the present invention, there is provided a subcarrier, bit and power allocation method for an ofdma system, comprising the steps of: distributing the number of the subcarriers based on the power reduction amount caused by adding one subcarrier to each user, thereby determining the number of the subcarriers required by each user; calculating the average bit number sent by each user on one subcarrier according to the determined subcarrier number of each user, and determining the subcarrier specifically allocated to each user according to the power value required by sending the average bit number; for each user, bit loading is performed according to a single-user water filling algorithm.

Drawings

The invention is further described in connection with preferred embodiments with reference to the accompanying drawings. Wherein:

fig. 1 shows a block diagram of an OFDMA system which can be used for the allocation method according to the present invention.

Fig. 2 shows a flow chart of a resource allocation method according to the present invention.

Detailed Description

Fig. 1 shows a system block diagram that can be used for the allocation method according to the invention. This system is an OFDMA system. Fig. 1 shows the subcarrier, bit and power allocation modules in the system in detail.

Fig. 2 shows a flow chart of a subcarrier, bit, power allocation method according to the present invention. As shown in fig. 2, the allocation method according to the present invention first determines the number of subcarriers required by each user by allocating the number of subcarriers according to the water-filling principle in combination with the average channel gain according to the power reduction caused by adding one subcarrier to each user. The subcarriers specifically allocated to each user are then determined based on the power value required to transmit the number of bits that each user transmits on average over each subcarrier allocated to it. And finally, carrying out bit loading according to a single-user water filling algorithm.

Each step in the allocation method according to the invention minimizes the transmission power in an average sense and such a three-step joint allocation scheme can also achieve a significant reduction in complexity.

The subcarrier, bit, power allocation method according to the present invention is described in detail below. Assume that there are K users and N subcarriers in the system. The bit number of user k to be transmitted is R_k。

In the first step, the number of subcarriers required by each user is determined.

It is first assumed that the number of subcarriers initially allocated to each user is 1. The process described in detail below is then performed to determine a user, and the number of sub-carriers allocated to this user is increased by 1. This determination is repeated until all N subcarriers are allocated.

This determination is described below:

assume that, for user k, the number of subcarriers allocated to user k is N before performing the determination process_kThen the average number of bits transmitted per subcarrier is R_k/N_kWherein R is_kThe total number of bits that need to be transmitted for user k. Suppose that user k is added with one subcarrier, N_k＝N_k+1, the average number of bits transmitted per subcarrier is R_k/(N_k+1). According to the following formulas (1) and (2):

wherein f is_k(r_kN) is r transmitted on subcarrier n by the receiving end in order to receive user k_k，nReceived power required for one bit, N₀Is the noise power spectral density, BER_kIs the bit error rate QoS requirement of the traffic.

P_{k, n} = \frac{f_{k} (r_{k, n})}{g_{k, n}^{2}} - - - (2)

Wherein, P_k，nFor the corresponding transmit power of the transmitting end, g_k，nIs the channel gain corresponding to the subcarrier. It can be obtained that when the number of subcarriers allocated to user k is from N_kIncreasing N_k+1Then R is transmitted within one OFDM symbol_kReduction of power required for one bit Δ P_kIs composed of

Wherein,

is the root mean square of the subcarrier channel gains assigned to user k, i.e.:

according to the above equation (3), the power reduction value Δ P when the number of subcarriers thereof is increased by 1 is calculated for all users_kAnd reducing the value Δ P from the power of all users_kThe maximum value is picked, that is, the number of sub-carriers allocated to the user corresponding to the maximum value is determined to be added by 1.

And then repeating the above determining process, and distributing the rest sub-carriers to the users one by adopting the same method for comparing the power reduction values until all the N sub-carriers are distributed.

And secondly, after the number of the sub-carriers required by each user in the system is determined, selecting the required specific sub-carriers from the sub-carriers available in the system for each user.

Suppose that for user k, the number of subcarriers allocated to that user is determined to be N in the previous step_kThen send on the nth sub-carrier (R)_k/N_k) The power required for each bit is:

P_{k, n} = \frac{f_{k} (R_{k} / N_{k})}{{g^{2}}_{k, n}} - - - (5)

thus, for each user and for each subcarrier, N x K power values P can be obtained_k，nComposed matrix P

By P_k，n ^*Representing the minimum value P in the matrix P_k，n. Finding P_k，n ^*And allocates the corresponding subcarrier n to the corresponding user k because of the minimum value P_k，nMeaning that user k requires the least power to transmit information on subcarrier n. And set P_k，nInfinity. Continuing to find P in matrix P by the same method_k，n ^*Until each user is allocated the desired sub-carriersAnd (4) counting.

And a third step of loading the bit information to be transmitted by the user on the allocated sub-carriers. Since the sub-carriers allocated to the users have been determined by the first two steps, a single-user water-filling algorithm can be used for bit loading. Define by Ω_kDenotes the set of sub-carriers, Δ P, to which user k is allocated_k，nFor user k, in subcarrier n (n belongs to Ω)_k) The amount of power increase when more than one bit is loaded, i.e.

Find out omega_kMiddle smallest Δ P_k，nAnd adding 1 to the corresponding subcarrier by the transmitted bit number. Repeating the above process, and loading the bits to be sent of user k to omega_kOn the sub-carriers of (a). The bit loading method of other users is the same.

The complete procedure of the subcarrier, bit, power allocation method according to the present invention has been described in detail above.

However, in the allocation method according to the present invention, in order to further reduce the computational complexity, the second step, i.e. the step of determining specific subcarriers for the user, may be modified.

Because of the information transmittedThe required power is mainly given by the channel gain g_k，nSo that the channel gain can be substituted for the transmit power, i.e. the matrix P mentioned above is replaced by the following matrix G

However, due to P_k，nAnd g² _k，nInversely proportional, so in this case, g needs to be determined_k，nIs measured. By g_k，n ^*Represents the maximum value g in P_k，n. Find out g^k，n ^*And allocates the corresponding sub-carrier n to the corresponding user k because of the maximum value g_k，nMeaning that the signal gain of user k is the largest for n on the sub-carriers and thus that the power required by user k to transmit information on n on the sub-carriers is the least. Set up g_k，n═ infinity. The same method is adopted to continuously search for G in the matrix G_k，n ^*Until each user is allocated the required number of sub-carriers.

It can be known from theoretical analysis and computer simulation experiment verification that the subcarrier, bit and power allocation method according to the invention has obvious advantages in terms of saving transmission power and information processing complexity compared with the multi-user greedy water injection method in the prior art, especially under the conditions that the number of information bits of each user is fixed and the number of users is changed, and under the conditions that the number of users in the system is fixed and the number of information bits of each user is changed.

Claims

1. A sub-carrier, bit and power distribution method for an orthogonal frequency division multiple access system comprises the following steps:

distributing the number of the subcarriers based on the power reduction amount caused by adding one subcarrier to each user, thereby determining the number of the subcarriers required by each user;

calculating the average bit number sent by each user on one subcarrier according to the determined subcarrier number of each user, and determining the subcarrier specifically allocated to each user according to the power value required by sending the average bit number;

for each user, bit loading is performed according to a single-user water filling algorithm.

2. The method of claim 1, wherein the subcarrier number allocation step comprises:

calculating a power reduction value caused when each user adds a subcarrier;

determining a maximum of the calculated power reduction values;

and adding 1 to the number of the sub-carriers allocated to the user corresponding to the maximum value.

3. The method of claim 2, wherein in the subcarrier number allocation step, an initial value of the number of subcarriers allocated to each user is 1; and repeating the subcarrier number allocation step until all the subcarriers are allocated.

4. A method according to any of claims 1 to 3, wherein the step of determining the sub-carriers specifically allocated to respective users comprises:

respectively calculating the power required by each subcarrier for sending the average bit number of each user;

determining a minimum value of the calculated powers;

allocating the sub-carrier corresponding to the minimum value to the corresponding user, and setting the minimum value to infinity, wherein the sub-carrier can not be allocated to other users;

the previous two steps are repeated until each user is allocated the determined number of subcarriers.

5. A method according to any of claims 1 to 3, wherein the step of determining the sub-carriers specifically allocated to respective users comprises:

respectively determining the channel gain corresponding to each subcarrier when each subcarrier is allocated to each user;

determining a maximum value of the determined channel gains;

allocating the sub-carrier corresponding to the maximum value to the corresponding user, and setting the maximum value to be infinitesimal, wherein the sub-carrier can not be allocated to other users;

6. The method of claim 1, wherein the bit loading step comprises:

calculating the power increment of each subcarrier allocated to a user when one bit is additionally loaded;

determining a minimum value of the calculated power increase amount;

and adding 1 to the bit number of the subcarrier corresponding to the minimum value.

7. The method of claim 6, wherein in the bit loading step, an initial value of the number of bits allocated to each subcarrier is 1; and repeating the bit loading step until all bits are loaded.